Electric smelting furnace

ABSTRACT

A three-phase electric smelting furnace having three electrodes arranged to form the apices of a triangle, and having material chargers. Each electrode has a plurality of the material chargers exclusively and operatively connected thereto. The lower end openings of the material chargers for each electrode are disposed along a concentric circle in symmetrical spacing with each other. The lower end openings of different groups of material charger for different electrodes are also disposed symmetrically with respect to the groups. Each material charger has a means for measuring or measuring and recording the change in the quantity of the materials therein. It is possible to attach a pretreating means to the material chargers for preheating, drying, calcining, or prereducing the materials.

United States Patent [72] inventors Minami-ku, Nagoya,

[54] ELECTRIC SMELTING FURNACE 2 Claims, 4 Drawing Figs.

[52] U.S.Cl 13/33 [5]] lut.Cl F27d3/l0 [50] FieldolSearch l3/2,9,33,

[56] References Cited UNITED STATES PATENTS 1.807.090 5/l93l Pistor13/33 $163,520 l2/l'964 Collin etal. l3/33 Primary Examiner Bernard A,Gilheany Assistant Examiner-R. N. Envall, Jr. A1l0rney-Waters. Roditiand Schwartz ABSTRACT: A three-phase electric smelting furnace havingthree electrodes arranged to form the apices of a triangle, and havingmaterial chargers. Each electrode has a plurality of the materialchargers exclusively and operatively connected thereto. The lower endopenings of the material chargers for each electrode are disposed alonga concentric circle in symmetrical spacing with each other. The lowerend openings of different groups of material charger for differentelectrodes are also disposed symmetrically with respect to the groups.Each material charger has a means for measuring or measuringr'andrecording the change in the quantity of the materials therein. it ispossible to attach a pretreating means to the material chargers forpreheating, drying, calcining, or prereducing the materials.

PATENTEU Aum Olen 3,588,888

sum 1 [IF-3 PATENTED AUG] 01971 SHEET 2 [IF 3 FIG.3

ELECTRIC SMELTING FURNACE This invention relates to a three-phaseelectric smelting furnace having three electrodes arranged to each formthe apex of a triangle for smelting pig iron, ferroalloy, nonferrousmetals and chemical products, such as calcium carbide, and moreparticularly to a closed type electric smelting furnace having specialmeans for charging the materials to be smelted therein.

An object of the present invention is to provide an electric smeltingfurnace characterized in that the furnace comprises electrodes, groupsof material chargers, each group of said charge equipments belongingexclusively to corresponding one of said electrodes, respectively, andarranged in such a manner that lower end or discharge openings of saidmaterial chargers in each group are disposed along a concentric circlearound the corresponding electrode in symmetry with respect to theelectrode, and at the same time to lower end openings of adjacent groupsof said material chargers with each other, and a means for substantiallycontinuously measuring or recording the feeding rate, or the change inthe quantity of the materials stored in each ofsaid material chargers,whereby the material consumption for each electrode and materialchargers can be observed continuously-as smelting proceeds.

In a preferred embodiment of the present invention, high temperature gassubstantially free from oxygen is delivered through the materials ineach of said material chargers, whereby the materials are preheatedand/or pretreated.

Other objects and a fuller understanding of the present invention may behad by referring to the following description taken in conjunction withthe accompanying drawings, in which:

FIGS. 1 and 2 are examples of sectional plans of the roof level of anelectric smelting furnace having three electrodes and actuated by athree phase A.C.- power source, according to the present invention;

FIG. 3 is a sectional elevation taken along a line abode of FIG. 1; and

HG. 4 is a chart showing an example ofcurves recorded by measuring theweight change of the materials stored in each material charger assignedfor each electrode.

Like members and parts are designated by like numerals and symbolsthroughout the drawings.

In the following description of the present invention, an embodiment isdescribed with reference to a closed type electric smelting furnace withthree electrodes actuated by a three phase AC power source, eachelectrode having six material chargers belonging exclusively thereto. Itshould be understood that the embodiment is described and illustrated bymere way of an example, and the present invention is not restricted tosuch embodiment.

Referring to FIGS. 1 and 2, illustrating plans at the roof level of thefurnace, three vertical electrodes I, II, and III are disposed in thespace defined by a furnace wall 7, in a conventional manner, so as toform apices of an equilateral triangle. The figures also illustrate thedisposition of the lower end openings of the material chargersoperatively connected to each electrode.

The material chargers belonging exclusively to the electrode I, ll andill have the lower end openings 1,2, 3, 4, 5, 6, l', 2', 3', 4', 5', 6',and l", 2", 3", 4", 5", 6", respectively.

The material chargers belonging exclusively to the correspondingelectrode have the lower end openings disposed along a concentriccircle, and in symmetry with respect to the axis ofeach electrode. Thelower end openings ofthe material chargers belonging exclusively toadjacent electrodes, e.g., l and II, respectively, are also disposed insymmetry with each other. Due to said arrangement of the lower endopenings, each material charger can exclusively feed the materials tothe corresponding electrode uniformly along symmetrical directions andsubstantially not to the other electrodes.

Referring to FIG. 3, illustrating a sectional elevation along the lineabcde of FIG. 1, each material charger of the illustrated embodiment ofthe invention comprises a storage tank for temporarily storing thematerials, and a trough pipe for feeding the materials from the storagetank to the furnace. In the figure, it is apparent from the dispositionthat the materials stored in the storage tank 8, passing through thetrough pipe 12 and the lower end opening 4 at the side of the furnacewall 7, are fed exclusively to the electrode I. In the same way, thematerials stored in the storage tank 8' are fed exclusively to theelectrode II.

In the following description, for the sake of simplicity, the storagetanks and the trough pipes are unified and referred to as the materialscharger, unless otherwise specified.

The lower end openings 6 and 2' of the material charger disposed betweenthe electrodes 1 and I] feed the materials exclusively to thecorresponding electrodes I and II, respectively, and substantially notto the other electrodes, due to the positions of the lower end openingsof the material charger relative to the corresponding electrodes as wellas the angle of repose of the materials fed in the furnace, unlessdisturbances, such as hanging of the materials, take place.

Referring to FIGS. 1 and 2, those material chargers which are disposedcloser to the center of the furnace than the rest, i.e. materialchargers having the lower end openings 1, l, l" in FIG. land 1,1, 1",6,6, 6" in FIG. 2 are also disposed in such a manner that they feed thematerials exclusively to the corresponding electrodes, and substantiallynot to the others, although they are not shown in FIG. 3. Furthermore,due to the symmetrical disposition of the group of material chargersbelonging to one electrode with respect to the other groups belonging tothe adjacent electrodes, each electrode receive the entire quantity ofthe materials to be smelted by the electrode from those materialchargers belonging thereto.

The number of the material chargers for each electrode is not restrictedto six, as depicted in FIGS. 1 and 2, but four or more material chargerscan be used for each electrode, depending on the size of the furnace. Itis preferable, however, to use not less than live material chargers perone electrode.

In the illustrated embodiment, the lower end openings belonging to aparticular electrode are disposed symmetrically along a circle aroundthe electrode, but the disposition of the lower end openings accordingtothe present invention is not always limited to strictly symmetricalone. For instance, if the pressure of the materials fed from each lowerend opening into the furnace is balanced and does not act to force theelectrode away, the lower end openings belonging to an electrode do notalways need to be arranged exactly along a concentric circle around theelectrode, or to be symmetrically disposed at equal intervals.

It has been widely practiced to provide material chargers in electricsmelting furnaces. However, except single phase electric smeltingfurnaces, the usable space above the furnace is extremely limited due tothe electric bus conductor arrangement with a conventional construction,for instance in the case of three phase-three electrode furnace.Accordingly, the number of material chargers for each electrode is alsolimited. In fact, in conventional furnaces, a common material charger isusually disposed in the space between adjacent electrodes or at thecenter of the furnace for feeding the materials to two or threeelectrodes in common. There have not yet been any known polyphaseelectric smelting furnaces having a plurality of material chargersbelonging exclusively to individual electrodes, respectively.

Thus, the electric smelting furnace, according to the present invention,is featured firstly in that there is provided a plurality of materialchargers belonging exclusively to each electrode. The second featureofthe electric smelting furnace, according to the present invention, isin that the weight change of the materials in each material charger orthe feeding rate of the materials through each material charger into thefurnace is continuously measured for watching. By combining these twofeatures, outstanding effects can be achieved in controlling theoperation of the electric smelting furnace.

The quantity or amount of the materials in each storage tank can bemeasured by the volume, height, or weight of the materials therein.There are a number of known methods for measuring them; namely, a methodusing suspending weight, a method using static capacitance, a methodusing the piezoelectric effects due to the weight, a method usingisotopes, etc. Among conventional measuring methods, those for measuringthe weight of the materials are preferably used, in the electricsmelting furnace according to the present invention, for continuousmeasurement ofthe material quantity, and for recording the change of theamount of the materials as a continuous curve. The same effects areachieved by intermittent measuring and/or recording with appropriatetime intervals, instead of absolutely continuous.

In the illustrated embodiment, a weight measuring means is mounted oneach storage tank as shown in FIG. 3. The weight measuring means willnow be described on the measuring means mounted on the storage tank 8corresponding to the lower end opening 4 belonging exclusively to theelectrode 1, which is substantially the same as the measuring meansmounted on the other material chargers.

In FIG. 3, the bottom of the storage tank 8 is contracted in a funnelshape, and a weight measuring means 10, such as astrain-electroresisting element, is mounted on a support structure 9.The funnel shape bottom of the storage tank 8 is connected to the troughpipe 12 by a flexible joint 11 such as a bellows type, and the lower endof the trough pipe 12 is fastened to a furnace roof 13 to form the lowerend opening 4 of the material charger.

The funnel shape bottom of the storage tank 8 is made to facilitate themeasurement of the weight of the materials therein. By properlydesigning the funnel shape bottom of the tank 8, based on soilmechanics, which is not essential to the present invention and notdescribed in detail here, the weight of the materials in the storagetank 8 can fairly accurately be measured without disturbing the smoothfeeding of the materials therethrough. 7

When it is difficult to dispose the trough pipe I2 vertically inalignment with the axis of the storage tank 8, due to space limitationabove the furnace caused by the electric bus conductor arrangement, thetrough pipe 12 can be slanted at a suitable angle, which may be largerthan the angle of repose of the materials. And the storage tank 8 can bedisposed outside the periphery of the furnace roof 13. The storage tank8 and the trough pipe 12 are not always restricted to be a straightshape, but if due care is taken in design, curved shape can be adopted.When there is a sufficient space for the material chargers above thefurnace, the trough pipe 12 can be shortened or dispensed with byconnecting the flexible joint 11 to the furnace roof 13 for directlydelivering the materials from the storage tank 8 into the furnace.

The weight measuring means is connected to a weight indicator andpreferably to a weight recorder, so that the change in the amount of thematerials in the storage tank 8 in response to the progress of smeltingcan be continuously indicated and/or recorded. FIG. 4 illustrates anexample of a weight recording chart thus measured.

In the chart of FIG. 4, the materials in the storage tanks correspondingto the lower end openings l, 2, 3, 4, 5, and 6 belonging exclusively tothe electrode 1 decrease in weight almost at the same rate, whichclearly shows a fact that the electrode l carries out smelting uniformlyall around the electrode.

The chart of FIG. 4 also shows that the storage tanks are recharged withthe materials after three hours.

Referring to the curves related to the electrode II, the materialsthrough the lower end openings 3', 4, and 5' are smelted substantiallyat the same rate as those of the electrode 1, but the materials throughthe lower end openings 1, 2, and 6' slower. Thus, smelting around theelectrode II is not quite smooth and somewhat slower than that aroundthe electrode 1.

As regards the electrode lll, smooth smelting is carried out at first,but smelting of the materials through the lower end openings 3", 4", and5" becomes somewhat slowed down after one hour to two, and the materialsto be smelted through such troubles are left as they are, the furnacecondition becomes worse and some serious accidents may be resulted.Therefore, proper and corrective treatments must be taken quickly.

Thus, continuous measurement of the amount of the materials in eachmaterial charger belonging exclusively to corresponding electrodes makesit possible to watch exactly and control effectively the smeltingconditions at various portions around each electrode.

In the preceding description, the change in the amount of the materialsis measured continuously, but the measurement can also be madeintermittently with short intervals, although continuous measurement andrecording are preferable.

If there should be any symptom of abnormal conditions, such abnormalityis easily noted at the early stage, so that proper countermeasures canbe taken quickly, such as additional charge of reducing agents, poking,etc. It is also possible to change the mixing ratio of the materials tobe fed to the specific portions of the furnace according to the smeltingconditions. It should be noted that such change can be carried outwithout affecting the other portions. Thus, the abnormality of suchportions can be removed quickly at the earliest stage.

Generally speaking, in a closed type electric smelting furnace withknown methods of material feeding, it is impossible to inspect directlythe inside of the furnace with the eyes, and the conditions within thefurnace are conjectured barely by temperatures measured under thefurnace roof and the other deficient methods. Such temperatures may beaffected by heat from the other portions within the furnace, so thatexact temperatures at the specified part cannot be obtained. Thus, it isdifficult to take proper countermeasures for abnormal conditions at theearly stage, and as a result serious troubles are apt to take placerather frequently.

The inventors succeeded in constructing and operating a large closedtype electric smelting furnace for 50 percent Si ferrosilicon with acapacity of 45,000 KVA, which is the largest in the world at thepresent. In order to ensure sufficient space above the furnace fordisposing the charge equipments, it is preferable to use the electricbus conductor arrangement according to the invention A Bus ConductorSystem for a Three Phase Electric Furnace filed under the applicationnumber of U.S. Pat. application Ser. No. 740,237. In fact, the electricbus conductor arrangement according to said inventions was applied tosaid large capacity electric smelting furnace, so as to arrange the busconductors in orderly and compact fashion. 7

Besides, with the arrangement according to said inventions, the smeltingelectric load characteristics can be easily be balanced among respectiveelectrodes in the furnace, so that the conditions within the furnace canbe controlled smoothly.

The electric smelting furnace according to the present invention hasother interesting effects. By continuously measuring the weight changeof the materials fed into the furnace, the smelting rate cancontinuously be determined exactly. Thus, the smelting rate orproductivity for respective electrode and for the entire furnace can bereadily calculated. It is also possible to determine instantaneouselectric power consumption per unit weight of products by dividing theelectric power load by the productivity. Thus, various data useful forthe control of the furnace operation can easily be obtained.

Apart from said method, similar effects may be obtained, for instance,by measuring continuously or frequently the weight of the materialsbefore charge into the material chargers, keeping a stock level of thematerials therein constant.

The material chargers according to the present invention can also beutilized for pretreatments of the materials, such as drying, preheating,calcining and prereducing, etc., so as to save electric powerconsumption and reducing agents as well as to increase the productivity.By utilizing such pretreatments, the effects of the present inventioncan be remarkably improved. Referring to FIG. 3, for instance, suchpretreatments can be conducted as follows, A closing bell 16 is providedat a funnellike hopper at the top of the storage tank 8, and gastightlycloses the upper end opening of the storage tank 8, except the period ofcharging the materials into the storage tank 8 through the hopper 15,while providing a gas inlet 17 at a funnellike receiving hopper 14secured at the top of the trough pipe 12 and connected to the storagetank 8 by the flexible joint 11. A gas outlet is mounted at the upperpart of the storage tank 8. The materials in the storage tank 8 can bepretreated by introducing hot gas from the gas inlet 17 and dischargingit from the gas outlet 18.

Under usual conditions, where the pressures at the upper part of thestorage tank 8 and the lower end opening 4 are substantially equal andthe flow resistance through the trough pipe 12 is high due to a narrowsectional area thereof, only small amount of the gas goes into thetrough pipe 12, while most of the gas into the storage tank 8. In caseof a closed furnace, the hot gas thus entered into the furnace istreated together with the furnace gas through a cleaning system (notshown).

As the hot gases for the pretreatments, gas recovered from the furnaceor other gases are used after heated by a heatexchanger or burntpartially. It is essential that the hot gas is chemically reducing orinactive and substantially free from oxygen, because if the hot gascontains oxygen in excess ofa certain limit, the carbons in thematerials, such as coke and coal, tend to be ignited and burned. On thecontrary, the hot gas containing a large amount of reducing gas, such ascarbon monoxide and hydrogen, not only dries and heats the materialsdepending on the temperature and the amount thereof, but also effectspreliminary reduction and calcination.

The exhaust gas from the gas outlet 18 may be purged off after suitabletreatment, depending on the properties thereof. If the exhaust gashasother utilities, it may be reused after applying a suitable treatment,or by introducing into the cleaning system of the furnace gas in caseofa closed furnace.

In a closed furnace, the gas pressure under the furnace roof is usuallycontrolled to keep at a level slightly higher than the atmosphere.Accordingly, by properly controlling the pressure, for example, bysuctioning, at the upper part of the storage tank 8, the furnace gas canbe forced into the material chargers for pretreating the materials. Duecare should be taken to keep such pretreatments constant throughout thesmelting operation, the extent of which, such as preheating, calcining,and prereduction, affects the electric load characteristics of thematerials, such as electric conductivity thereof, as well as thesmelting conditions, Continuous measurement and control should be madeon the temperature distribution of the materials at various portions inthe material chargers, together with the composition of the hot gasintroduced therein and the flow rate of the gas at the correspondingportions.

It is possible to use a double mechanism at the funnellike hopper l5 andthe closing bell 16, so as to charge the materials into the storage tank8 without interrupting the hot gas flow. In the case ofa singlemechanism, as shown in FIG. 3, the flow of hot gas may be continued orinterrupted during the charge of the materials into the storage tank 8,depending on the composition of the hot gas.

It is also possible to provide the material chargers with specialfacilities for effecting the pretreatments of the materials bycirculating hot gas through such facilities.

In addition to said examples, such pretreatments can be applied to thematerials in the material chargers by other means.

In any case, if the hot gas temperature is below 200 C. effectivepretreatments cannot be achieved, and thus the temperature thereofshould preferably be as high as possible.

These portions of the material chargers exposed to high temperatureshould be provided with suitable protection against heat.

Saving of about 250 KWI-I in electric power consumption per l,000 kg. ofsmelted product, and at the same time corresponding increase inproductivity are achieved, by preheating the materials in the materialchargers to 500 C., with the electric smelting furnace of saidconstruction according to the present invention, under the followingconditions;

Materials per 1,000 kg. of product 2,500 kg. Average specific heat ofthe materials 0.25 kcal./kg. C. Average temperature of the materials 500C.

Heat loss 30 percent Although the present invention has been describedwith a certain degree of particularity, it is understood that thepresent disclosure has been made only by way of example and thatnumerous changes in details of construction and the combination andarrangements of parts may be resorted to without departing from thespirit and the scope of the invention as hereinafter claimed.

What we claim is:

l. A three-phase electric smelting furnace having three electrodesarranged to form the apices of a triangle, comprising three groups eachincluding a plurality of means for charging materials to said furnace,each group of charging means being associated with respectively one ofsaid three electrodes, each group being arranged so that the lower enddischarge openings of each of said charging means in each said group arepositioned in a generally concentric circle about their associatedelectrode and spaced symmetrically relative thereto and with respect tothe lower end discharge openings of the other adjacent groups of saidcharging means, and means for substantially continuously measuring thechange in the quantity of the charging materials contained in each ofsaid charging means.

2. A smelting furnace as claimed in claim 3, comprising means forsubstantially continuously recording material quantity consumption insaid furnace so as to facilitate constant surveillance of furnaceoperating conditions.

1. A three-phase electric smelting furnace having three electrodesarranged to form the apices of a triangle, comprising three groups eachincluding a plurality of means for charging materials to said furnace,each group of charging means being associated with respectively one ofsaid three electrodes, each group being arranged so that the lower enddischarge openings of each of said charging means in each said group arepositioned in a generally concentric circle about their associatedelectrode and spaced symmetrically relative thereto and with respect tothe lower end discharge openings of the other adjacent groups of saidcharging means, and means for substantially continuously measuring thechange in the quantity of the charging materials contained in each ofsaid charging means.
 2. A smelting furnace as claimed in claim 1,comprising means for substantially continuously recording materialquantity consumption in said furnace so as to facilitate constantsurveillance of furnace operating conditions.